Wet bulb thermostatic control



LAHWHHLn u AREFERENCE "R ZFT FIPBZIZ Oct. 8, 1940. R. T. PALMER 'ET BULB THERMOSTATIC CONTROL uodson 1li Qn.

Filed Feb. 18. 1939 MOEDOW MNP? Own-|210 Il QN Patented Oct. 8, 1940 WET BULB THERMGSTATIC CONTRO Robert 'l'. Palmer, Sharon, Mass., assigner to B. F.

Stm-tevant Haes.

Application February 18, 1939, Serial No. 257,209

8 Claimi- (CL 236-44) For a 65 F. wet bulb temperature, a psychrometric chart shows the following:

This invention relates to thermostats and relates more particularly to wet bulb thermostats. Wetbulb thermostats heretofore have either been of the type which includes a thermometer with a wetted wick around its bulb or of the differential type combining a hygrostat adjusted by a dry bulb thermostat to respond to wet bulb temperatures. The wick type thermostat has been unsatisfactory chiefly because of the dim- 10 culty of maintaining an adequate supply of clean water to the wick. The differential type is delicate and difcult to maintain in adjustment.

This invention provides wet bulb thermostats which are electrical and which do not depend upon evaporative or hygroscopic actions. In a preferred embodiment, a light source projects a beam of light reflected by a mirror upon a photoelectric surface. The mirror ls in the air which is to actuate the thermostat.

When acting as a wet bulb thermostat. an associated dry bulb thermostat exposed to the same air, adjusts the temperature of a fluid acting to cool the back of a mirror, to follow dry bulb temperature changes so that when the wet bulb temperature of the air rises above the control temperature, moisture' from the air condenses upon the mirror to interrupt the reilected light reaching the photo-electric cell causing it to actuate the controls. Y

An object of the invention is to provide an improved wet bulb thermostat.

The invention will now be described with reference to the drawing. of which:

5 Fig. 1 is a diagrammatic view of one embodiment of the invention included in an air conditioning system for a railway passenger car, and

Fig. 2 is a diagrammatic view of another embodiment of the invention including its own re- 40 frlgeration plant.

In railway car conditioning systems, for ,example, it is desired to .convert an air washer system from refrigerative cooling toevaporatlve cooling when the wet bulb temperature is at or below say 65 F., and to convert the system from evaporative cooling to refrigeratlve cooling when the wet bulb temperature isabove 65 F. A wet bulb thermostat in the outdoor air stream usually adjusts the dampers to 100% outdoor air when the wet bulb temperature is at or below the desired control temperature, and adjusts the dampers to about 25% outdoor air and '75% recirculated air when the wet bulb is above the control l temperature.

Company, Hyde Park, Boston,

When .the wet bulb temperature rises above F., then moisture will condense at the above dew point temperatures for the temperatures given above. If therefore,

respective dry bulb surface is chilled to temperatures just below the dew point temperature corresponding to the dry bulb temperature and 65 wet bulb, moisture will condense out of the air upon it when the wet bulb temperature of the air rises above 65 F. According to this invention, a dry bulb thermostat adjusts a thermostat controlling the temperature at the mirror surface to cause it to be chilled to temperatures just below the dew point temperature for 65 F. wet bulb temperature and the prevailing dry bulb temperature.

In Fig. l, outdoor air drawn in by the blower l for supply to the air cooler l, passes between the shutters 'l in contact with the dry bulb thermostat l and the mirror surface 8. Recirculated air from the passenger space passes through the shutters lll into the blower 6.

'I'he pump Il draws chilled water from the source l2 and supplies it through the pipe Il to the air washer 6. The water is recirculated from the washer through the pipe I4 and sump Il to the source I2 for recooling.

The mirror surface 9 forms one side of a compartment i6 through which chilled water from the source is circulated by the pump Il through pipes Il and l1, mixing valve Il and pipe I9. the water from the compartment through the pipe 10 to the source i2. 'I'he pump 2l draws warm water from the sump I5 and supplies it through the pipe 2v2 to the mixing valve i6 where it mixes with the chilled water from the source I 2, for supply through the pipe I9 to the compartment I6. The mixing valve il is of the well known type containing a thermostat for adjusting orifices connecting with vits two inlets for controlling the mixture of the water within the valve for maintaining the leaving water at the desired temperature.

'I'he dry bulb thermostat l adjusts the bellows I6 returning 23 which is connected by the tubing 24 to the UIUO ILV LHLHU.

is well known. As the dry bulb temperature of s the outdoor air changes, the thermostat 23 adjusta thethermostatinthevalve Iltocauseitto mixthechilledwaterfromthesourceand the warm water from the sump Ii in the correct proportions for causing the temperature of the water in the compartment il to be about a'fourth of a degree below the dew point temperatme shown by standard psychrometric charts for 65 l'. and the prevailing dry bulb temperature.

Il the wet bulb temperature of the outdoor air 1| rises appreciably above 65 F., moisture will condense upon the outer surface of the mirror I and will interrupt the light beam from the light source, reflected by the mirror upon the photoelectric cell 21. The cell 21 then acts to deener- U gine the relay Il causing it to open its contacts to disconnect the shutter control motor from the electric source Il. This causes the motor to shift the dampers from 100% outdoor air to 75% recirculated air and 25% outdoor air by partially clonng the shutters I and by partially opening the shutters Il.

When the wet bulb temperature of the outdoor air drops to or below 65 F., the moisture onthemirroriswipedanddriedoifbytheair passing it and the photo-electric cell is again actuatedtoenergizetherelay Iltocauseitto close the energizing circuit of the motor 29 to cause it to again adjust the shutters for 100% outdoor air.

The embodiment of the invention described in the foregoing, makes use of equipment which is now in use on air conditioned railway cars. Fig.

2 illustrates an embodiment which may be self ,contained as for use at isolated points where it would not be convenient or feasible to supply refrigeration from the source for the air cooler.

Fig. 2 illustrates a small compressor-condenser arrangement which may be designed for use with the wet bulb thermostat of this invention. With (s reference now to Fig. 2, the compartment Il contains the evaporator coils Il which are connected to the compressor l2, condenser $3 and expansion valve il, The thermostat 31 in the compartment il iscnnected in an electric circuit with the motor Il which drives the compressor 32, and the electric source and controls the temperature of the mirror I by starting and stopping the compreasor.

The thermostat l1 is adjusted by the dry bulb thermostat through the intermediary of the bellows 23, tubing 2l and bellows 25, previously described to cause the thermostat $1 to operate the compressor to produce in the compartment il. lower temperatures as the dry bulb temperature o at I rises, and to discontinue the operation of the compressor as the dry bulb temperature falls, the thermostat 31 being adjusted by the thermostat I to cause it to maintain in the compartment i6, temperatures slightly below the dew point temperatures shown by standard psychrometric charts for 65 F. wet bulb temperature and different dry bulb temperatures. The compartment Il of Fig. 2 could be air tight or filled with any suitable liquid.

The control temperature of 65 F., has been selected for purpose of illustration for the reason that it has proved satisfactory in a number of air conditioned railway passenger cars, and ob- 15 viousiy the thermostat could be adjusted for anyotbertemperatureasrequiredfosthedutyto beperformed.

While several of the invention havebeendeacribedfortbepmposeofillustration.itshouldbeunderstoodthattheinventionis nottobelimitedtotheexactapparaiaisandarrangementofapparatm described,asmanyde parturesand modiiicationsmaybesuggestedto thoseskilledintbeartwitboutdeparturefrom the spirit of the invention.

Whatiselaimedis:

1. Awetbulbthermostat adaptedtobemountedinanairstrcamcomprisingamoisturedetecting surface, mans for adjusting the temperatureofsaidsurface,meansincludingadrybulb thennostatadaptedtobeexpoaedtotheairin said stream for adjusting said nrst mentioned means for maintaining said surface atatemperature approaching the dew point temperature of air for a predetermined wet bulb temperature and the prevailing dry bulb temperature, and meansfor detectingthecondensation of moisture uponsaidsurface.

2. Awet bulb thermostat adaptedtobemountedinanairstreamcomprisingamoisturcdetectingsurface. means foradjustingthetemperature ofsaid surface, means includingadrybulb ther- I Aniliiiu.

mostatadaptedtobeexposedtotheairinsaid' stream for adjusting said first mentioned means for maintaining said surface at a temperature approaching the dew point temperature of air for a predetermined wet bulb temperature and the prevailing dry bulb temperahire, means for detecting the condensation of moisture upon said surface,

and control means actuated by said detecting means.

3. A wet bulb thermostat adapted to be mountedinanairstreamcomprisingamoisture detecting surface, means for adjusting the temperature of said surface, means including a dry bulb thermostat adapted to be exposed to the air in said stream for adjusting said first mentioned means for maintaining said surface at a temperature approaching the dew point temperature of air for a predetermined wet bulb temperature and the prevailing dry bulb temperature, and control means actuated by moisture upon said 4. A wet bulb thermoat adapted to be mounted in an air stream comprising a moisture detecting surface, means for adjusting the temperature ofsaidsin'face.meansincludingadrybuibther mostatadaptedtobeexposedtotheairinsaid stream for adjusting said iirst mentioned means for maintaining said surface at a temperature approaching the dew point temperature or the air for a predetermined wet bulb temperature and the prevailing dry bulb temperature. and means including a photo-electric cell for detecting the condensation of moisture upon said surface. 5. Awetbulbthermostatadaptedtobemount- -ed in an air stream comprising Io. moisture detecting mirror, means for adjusting the temperature of said mirror. means including a dry bulb thermostatadaptedtobeexposedtothe air in said stream for adjusting said first mentioned means for maintaining said mirror at a temperature approaching the dew point temperature of the air for a predetermined wet bulb temperature and the prevailing dry bulb temperature, and means including a photo-electric cell for detecting the condensation of moisture upon said mirror.

6. A wet bulb thermostat adapted to be mounted in an air stream comprising a moisture detecting surface, means for adjusting the temperature o! said surface, means including a dry bulb thermostat adapted to be exposed to the air in said stream for adjusting said iirst mentioned means for maintaining said surface at a temperature approaching the dew point temperature of the air for a predetermined wet bulb temperature and the prevailing dry bulb temperature,

means including a photo-electric cell for detecting the condensation o! moisture upon said surface, and control means actuated by said last mentioned means.

'7. A wet bulb therm t adapted to be mounted in an air stream comprising a moisture detecting mirror, means for adjusting the temperature o! said mirror, means vincluding a dry bulb thermostat adaptedtobeexposedtotheairin said stream for adjusting said nrst mentioned means for maintaining said mirror at a temperature approaching the dew point temperature oi the airjior a predetermined wet bulb temperature and the prevailing dry bulb temperature, a lamp for projecting light upon said mirror, and means including a photo-electric cell exposed to light reiiected by said mirror from said source for detecting the condensation of moisture upon said mirror.

8. A wet buib thermostat adapted to be mount. ed in an air stream comprising a moisture detecting mirror, means for adjusting the temperature of said mirror, means including a dry bulb thermostat ior adjusting said nrst mentioned means for maintaining said mirror at a temperature approaching the dew point temperature oi air for a predetermined wet bulb temperature and the prevailing dry bulb temperature, a lamp for projecting light upon said mirror, means including a photo-electric cell exposed to light reiiected by said mirror from said source for detecting the condensation of moisture upon said mirror, and control means actuated by said detecting means.

RQBERT T. PALMER.. 

